Guy I wonder if anybody can shed some light.

Car started yest morning but as soon as I went to reverse out of my drive she dies. I try to restart and she won't fire up. No time to look into then as I had work. I try again 8 hours later still no joy. I look over the usual culprits when I open up the air box leaving it open she starts. I'll leave her run & warm up turn her off then on couple of times starts every time great I dusted of the filter looked a bit dirty but not that old so popped her back in and drove the car to halfords and got a new air filter fitted it car still running fine. I went then and did a few things driving stopping driving again all fine problem fix right? Wrong went to start the car this morning before the wife work she starts good turn her off but then when my wife goes to drive her 15mins later she starts but the dies after about 3 feet. Again in have work so leave 8 hours try again today for me but with trouble. Again I go under her investigating and this time pull the fuel filter and its buzzing got all build up all over it but again its not that old. So I replace the fuel filter and now for the life of me I cannot get her to stay running. Previously had problems starting after a fuel filter change try all the usual tricks syringing to prime used a can and half of easy start (worked last time) but she just will not stay running but is it the filter or another problem? No DTC code seams to be worse when cold and no symptoms when she's been working. Help lol

I had similar issues to yourself only about a week ago, The problem turned out to be the Fuel Rail Pressure Sensor, then after that, I had air the the fuel filter/line.

Take a look at my thread here http://www.fordownersclub.com/forums/topic/69372-ford-focus-2006-18-tdci-p0089-continuation/ it may help you out.